The switched mode power supply (SMPS) is a well-known type of power converter that plays a crucial role for supplying modern electronic circuits with power. Several improvements of SMPS have devised ways to increase switching efficiency during high load conditions. An example of such an improvement is the concept of synchronous rectification used in modern SMPS. Synchronous rectification causes the SMPS to achieve high power efficiency at higher current levels. But synchronous rectification suffers from increased switching activity in a power train of the SMPS, which yields decreased efficiency at light load conditions compared to the normal diode rectification conventionally used in traditional SMPS.
Light-load efficiency of SMPS is becoming increasingly important for SMPS powered devices. Improved light-load efficiency helps save energy and extends the battery life of the SMPS powered devices.
Several methods exist in the art for improving light-load efficiency of the SMPS. An example of such a method is to reduce the circulation energy and associated losses by means of running the SMPS in a discontinuous conduction mode (DCM). Another example of a method is to reduce the switching losses by means of reducing the switching frequency at light-load conditions. The final example is aimed towards multiphase converters and the improvement during light-load conditions for these multiphase converters is achieved by shutting down unnecessary phases.
Another well-known method to increase light-load efficiency is to introduce a pulse skipping mode (PSM) of operation. The pulse skipping mode of operation usually involves starting skipping pulses when the duty cycle is below a defined minimum duty cycle. This involves operating the SMPS in discontinuous conduction mode (DCM), examples of this method can be found in application notes for common SMPS controllers such as the TPS61175 from Texas Instrument.
Yet another variant of the pulse skipping mode can be found in U.S. Pat. No. 7,075,280. This variant uses a constant on-time, which means that the off-time is changed and thereby the switching frequency of the SMPS.
Yet another solution is disclosed in US2006/0268974A1 which involves changing operation mode of the SMPS from CCM to DCM without changing the duty cycle of the switching signal.
A problem associated with embodiments of the prior-art solutions is that the DCM of the SMPS is entered during PSM of operation.